PHYSICS (P1b)

PHYSICS (P1b)

1. Conservation of Energy

   • Energy cannot be created or destroyed
   • Conservation of energy applies to all energy changes

2. Useful Energy

   • Useful energy is energy in the place we want it and the form we need it
   • Wasted energy is energy that is not useful energy
   • Useful energy and wasted energy both end up being transferred to their surroundings which become warmer
   • As energy spreads out, it gets more and more difficult to use for further energy transfers

3. Energy & Efficiency

   • The efficiency of a device = useful energy transferred by the device / total energy supplied to the device x 100%
   • No machine can be more than 100% efficient
   • Measures to make machines more efficient include:
     • Reducing friction
     • Air resistance
     • Electrical resistance
     • Noise due to vibrations

4. Electrical Appliances

   • Electrical appliances can transfer electrical energy into useful energy by the flick of a switch
   • Uses of everyday electrical appliances include:
     • Heating
     • Lighting
     • Making objects move (e.g. using electrical motor)
     • Creating sound and visual images
   • An electrical appliance is designed for a particular purpose and should waste as little energy as possible

5. Electrical Power

   • Power is rate of transfer of energy
   • P = E/t
   • Efficiency = useful power out / total power in (x 100)

6. Using Electrical Energy

   • The kilowatt hour is the energy supplied to a 1kw appliance in an hour
   • E = P x t
   • Total cost = number KWh used x cost per KWh

7. Cost Effectiveness Matters

   • Cost effectiveness means getting the best value for money
   • To compare the cost effectiveness of different appliances, we need to take the account of costs to buy it, running costs, and other costs (e.g. running it)

8. Fuel for Electricity

   • Electricity generators in power stations are driven by turbines
   • Coal, oil, and natural gas are burned in fossil fuel power stations
   • Uranium and plutonium are used as fuel in nuclear power stations, much more energy is released per kg from them than fossil fuels
   • Biofuels are renewable sources of energy; such as methane and ethanol can be used to generate electricity

9. The National Grid

   • The National Grid is a network of cables and transformers that distributes electricity to our homes from distant power stations and renewable power generators
   • Step up transformers are used to step up power station voltages to the grid voltage, and step down transformers are used to step down the grid voltage for use in our homes
   • The high grid voltage reduces energy loss and makes the system more efficient

10. The Nature of Waves

    • We use waves to transfer energy, and to transfer information
    • Transverse waves vibrate at right angles to the direction of energy transfer of the wave; all electromagnetic waves are transverse waves
    • Longitudinal waves vibrate parallel to the direction of energy transfer of the waves; a sound wave is an example of a longitudinal wave
    • Mechanical waves can be transverse or longitudinal waves

11. The Electromagnetic Spectrum

    • V = f x λ; V = wavespeed in metres per second' f = frequency in hertz; λ = wave length in metres

12. Red-Shift

    • Red-shift of a distant galaxy is the shift to longer wavelengths of the light from it, because the galaxy is moving away from us

13. The Doppler Effect

    • The Doppler Effects is the change in the observed wavelength (and frequency) of waves due to the motion of the source of the waves